1. Field of the Invention
The present invention relates to a brazing method of brazing a joint at the contacted surfaces of two base metals, which is especially effective for brazing a large joint.
2. Description of the Prior Art
In the description of the conventional method and the embodiments of the present invention, the embodiments of large size joints will be illustrated, because the present invention attains especially remarkable effect in the case of large size joints.
FIG. 1 shows a large size lap joint of copper bar as one example for the illustration including the relative dimension of the joint.
In FIG. 1, the reference numerals (1) and (2) respectively designate base metal plates made of copper, etc. which form a joint but may designate any metals capable of being brazed; (3) designates the clearance of the joint which is the space between the plates.
Heretofore, in a operation brazing the lap joint, the operator made an effort to uniformly heat all of the joint with a gas flame such as an oxygen-propane flame while disposing a brazing sheet in the clearance or feeding a brazing rod from the peripheral edge of the joint.
However, in accordance with the conventional brazing method, non-adhered parts or voids are formed in the clearance, whereby a suitable brazing operation could not be attained.
FIG. 2 is a schematic view of one example of the brazing condition of a joint brazed by the conventional brazing method which is observed by the X-ray test, wherein the reference numeral (4) designates adhered parts with a brazing alloy; (5) designates base metals; (6) designates non-adhered parts on which the brazing alloy is spread; and (7) designates voids on which the brazing alloy is not spread.
When the brazing is performed by the conventional brazing method, the percent of adhered area is usually in a range of about 60 to 70%.
Even though suitable flux is precisely prepared or a skillful operator carefully works the brazing, the percent of adhered area is about 80%.
It is considered that the gas and the impurities produced from the flux in the clearance (3) remain in the clearance (3) while clogging the discharging outlet because all surfaces of the joint are uniformly heated to reach the optimum temperature and the brazing alloy is fed from the peripheral part of the clearance (3) in the conventional brazing method.